How do you calculate rainfall distribution?
By calculating the product of the rainfall intensity and the duration (i.e., the rainfall depth) for each rainfall duration, the cumulative rainfall distribution can be derived. The rainfall intensity data can then be obtained as the difference between the successive cumulative rainfall depths.
What is Type 2 rainfall distribution?
NRCS Standard Type II and Type III Distributions The Type II pattern distributes 45 percent of the total 24-hour rainfall in the maximum one-hour while the Type III pattern distributes 40 percent of the total rainfall in the maximum one-hour.
How do you calculate a Hyetograph?
4. Convert to a hydrograph
- Multiply the rainfall excess by the catchment area (converts rainfall to a volume)
- Divide by the time step (to calculate volume per unit time)
- Ensure flow is allocated to the correct time step – the rainfall during a time step produces the instantaneous flow at the end of the time step.
How do you record rainfall data?
The standard instrument for the measurement of rainfall is the 203mm (8 inch) rain gauge. This is essentially a circular funnel with a diameter of 203mm which collects the rain into a graduated and calibrated cylinder. The measuring cylinder can record up to 25mm of precipitation.
What is a Type III storm?
The Type III storm represents areas bordering the Gulf of Mexico and Atlantic seaboard where tropical storms and hurricanes generate heavy runoff. The Type II storm is used in the remainder of the United States.
How do you make a rain hyetograph in Excel?
One can generate such a representation in MS Excel by selecting the ‘Excess Rainfall Hyetograph (in)’ column, and apply the ‘Insert’ –> ‘Charts/Column/2D’ option. Right click on the chart area, and go to ‘Select Data’, and edit the ‘horizontal axis labels’ by selecting the range of data in ‘Time (h)’ column.
How do you measure rainfall accurately?
The most accurate way to measure rainfall is to take a rain bucket of a known diameter (usually 12 or 24 inches) and place it on a scale. The scale subtracts the mass of the container from the mass of the rain.
What is AMC in hydrology?
The Soil Conservation Service curve number (CN) method commonly uses three discrete levels of soil antecedent moisture condition (AMC), defined by the 5-day antecedent rainfall depth, to describe soil moisture prior to a runoff event.
What is CN value in hydrology?
The runoff curve number (also called a curve number or simply CN) is an empirical parameter used in hydrology for predicting direct runoff or infiltration from rainfall excess.
Which is the Rain distribution for a project?
Most projects will use one of the predefined rainfall distributions listed below. The most common are the SCS/NRCS rainfallslisted at the top of the table. The easiest way to use these distributions is to define your rainfall events using the built-in event lookup table.
How can I create a synthetic rainfall table?
The easiest way to use these distributions is to define your rainfall events using the built-in event lookup table. With HydroCAD-10, you can also generate a synthetic rainfall distribution based on local precipitation frequency data. Details here. For special applications, you can create a custom rainfall table by hand.
How are rainfall distribution tables used in HydroCAD?
Rainfall Distribution Tables HydroCAD provides several options for defining the rainfall distribution to be used with the SCS or SBUH runoff procedures. Most projects will use one of the predefined rainfall distributions listed below. The most common are the SCS/NRCS rainfallslisted at the top of the table.
Which is the most common rain event in a table?
The most common are the SCS/NRCS rainfallslisted at the top of the table. The easiest way to use these distributions is to define your rainfall events using the built-in event lookup table. With HydroCAD-10, you can also generate a synthetic rainfall distribution based on local precipitation frequency data.